The Complete Guide to Anti-Squat
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- เผยแพร่เมื่อ 7 มิ.ย. 2024
- One of the most misunderstood aspects of suspension design are the anti- properties: anti-dive, anti-lift and particularly, anti-squat. This guide will explain what anti-squat is and how to correctly figure out how much you have in a suspension.
Chapters:
Introduction 0:00
Acceleration Force 1:22
Car Example 1:37
Weight Transfer 2:22
Anti-Squat - Suspension in a Slot 3:22
The Perfect Slot Angle 4:59
The Effect of Drive Torque Split 6:46
Side View Instant Center 8:00
Reaction Torque 8:40
Drawing The Anti-Squat Line 10:23
Anti-Squat Percentage 11:17
Alternative Method 12:03
Conclusions 13:29
Huibert Mees
Suspensions Explained
Really should try rewatching this whilst less sleep deprived lol
I’m there
I came her from Matt's recent video, I will definitely watch some more videos on here!
Welcome!
SuperFastMatt sent me as well
Clear, simple, brilliant
Boom another highly concise and informative one thanks a lot sir
Brilliant, clear explanation. thank you!
Brilliant, clear explanation, clear pronunciation, very enjoyable! Thanks!
Wow I haven't understood anti-squat for so long, this was an amazing explanation!
The kind of a channel that I've been looking for so long.. great videos! Thanks for your great explanation 😊
brilliant explanation for anti-squat. thank you!
OMG this is so enlighting, I've never seen any content that as specific like this! Thank you, sir!
Thank you for your kind words and you're welcome. There's much more to come.
Great video! I would add that upper a-arms also effect jacking when they are present and in most instances override or counter the jacking effect of the lowers.
Great stuff. I didn't know about the distinction in anti-squat with IRS vs live axle, and the explanation of AWD vs RWD was also new for me. Anti-squat is something I want to look at on my BRZ. Common wisdom in the community is that it has too much because its rear suspension comes from the Impreza.
Thank you for finally shows how it actually works instead of just saying "do this to find this"!
Great great video. Thank you!
New subscriber! Nice explanation!
we need a video on dive, and lift....good coverage
I’m glad Matt recommend your channel, you explain things well.
How do the principles apply with leaf springs and traction bars on a straight axle car?
I understand the traction bar is really to keep the spring from wrapping up. Would you move the front spring eye up or down to adjust anti-squat? Also how would the regular spring shackles vs a slider at the rear of the spring affect the anti-squat.
The principles are exactly the same. Keep in mind that with a solid axle, the line needs to be drawn from the tire contact patch, not the wheel center.
Just stumbled onto your channel, you're doing a very good job! One thing that confused me though, if you look at Race Car Vehicle Dynamics page 631, it seems you don't find the instant center by drawing lines through the chassis mounts, but rather the continuation of the A arms untli you're laterally in the center of the wheel. I.e. with parallel wishbones, your instant center would be correct, but with the angled upper wishbone, the upper line would be offset vertically, imagining the upper wishbone to extend all the way until the tire center line, and your instant center would be a bit further to the left.
Niels, Yes, that is correct but it really only becomes an issue if the sideview angle of the arms is very severe which it rarely is. With more conventional arm angles, the error is small and can be ignored. To me, what it really points to is that the second method, which looks at the motion of the contact patch, is really the preferred method and it is what is done by all multi-body dynamic software systems that I have used. It's far more accurate and doesn't care what the suspension architecture is.
@@suspensionsexplained Thanks for your reply! I like how you present it, the sliding pin example as well. Hope you get more views in the future. There is a lot of popular superficial vehicle dynamics on youtube, often including mistakes, so it is refreshing to see your stuff.
Really good stuff! I wonder how thiis affects ghe job of the dampener/shock absorber? Do you want anti squat if the track is uneven?
Great explanation. The piece I'm still trying to wrap my head around is how much anti-dive or anti squat or anti-roll do I want in a design? Could you do a video talking about that a bit?
Very interesting and clear.
What about if it was a Portal axle, where the center of the axle shaft is not the center of the wheel hub?
Good question. It would certainly be different. The way to think it through is to picture the vehicle up against a wall. Apply torque from the engine and see what happens. The car can't move because of the wall so the engine just torques up the wheel. In a normal independent suspension, the wheel would try to turn but couldn't because of friction with the road. the result is that the engine torque just tries to push the suspension forward at the wheel center. With a portal axle, you still have the force pushing the wheel center forward, but there is also the gears in the hub where the gear attached to the input shaft is trying to "walk" around the gear attached to the wheel, so there is a moment being generated inside the knuckle/hub. The size of that moment also depends on the gear ratio of the portal axle and the type of gears: is it a simple two piece gear reduction or is it a planetary set, in which case the input shaft may actually spin in the opposite direction compared to the wheel. All of these factors would influence how the anti-properties would be affected by a portal axle setup. Sorry, there are never easy answers!
You explain this well. Do you teach at a school?
Matt Brown sent me! Glad I found your channel. If I may make a request: could you do a video discussing preload and how it effects ride comfort?
Thanks for the suggestion. This will be part of a larger bushing topic that I will cover in the future.
@@suspensionsexplained Thank you. Looking forward to it
Hello! Could you please elaborate more on why the reaction point is different between live axle and independent suspension? I am doing a research, if you can please point me out if you know literature which expands on the physics behind this. thank you very much
The Yamaha Tenere 700 utilizes anti-squat. Front wheel traction is important when riding motorcycles off-road to steer/counter-steer using throttle. Helps alleviate rear suspension from compressing and rebounding too quickly, causing a highside crash which can launch the rider clean off the bike.
Can you please make a video explaining how the rear wheels toe in/out during squat and why. For example the Nissan Skyline toes in during squat, and the BMW e46 toes out during squat. What causes this to be different?
I am building a drift car and would like to better understand how this difference will effect handling.
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A lot of "tutorials" often depict F1 cars, which I assume have an IRS ;) They create an instant center but then draw the line from that center to the contact patch (example suspensionsecrets) -- that is incorrect then?
Yes, that is incorrect. With an IRS, the line is drawn from the wheel center, not the tire contact patch.
If a vehicle were equipped with electric hub motors, would it be modeled as an independent suspension or a live axle? Thank you for the excellent content! You have a new subscriber
Or would need modeled as a live axle because the torque reaction is going through the suspension.
Do we draw the line for the perfect angle from the contact patch to the front axle / CG point regardless of where the differential is mounted?
You make me immediately want to go back to college, if you don't teach professionally you certainly should
This video illustrates a solid axle real differential but that setup is omitted from the roll center video. Does anybody know of a good video about the rear roll center with a solid axle and panhard bar?
Thanks
hello sir can you post a series on DESIGNING A SUSPENSION GEOMETRY FOR A FSAE CAR - DOUBLE WISHBONE, DAMPER TO LOWER ARM TO BODY or PUSH ROD SUSPENSION,
I will be waiting sir
i request you sir
Does this work the same way for front wheel driven cars?
you explained what it is quite well - but I was expecting you to show how push rods and pull rods are changed to actually perform this function. - move this forward and you increase anti squat for example....
Excellent explanaition, even though200/25 is not 80, 2000/25 is, so i understand what you mean! Kgm ( kilogram meter is a very good definition of torque, 1kgm=1kg, one meter from center of rotation.
I've been told that independent suspension cannot have strong enough anti-properties (particularly anti-squat) without making other responses like the roll centers and various geometry gains far less than ideal. Is this the case, and if not, which independent suspension designs are there that can be used both front and rear that allow you to independently control as many responses as possible?
The instant centers are independent of other properties like camber gain, toe change, or roll center height because those are properties that happen in the other dimensions. i.e., camber change happens in the rear view, toe change happens in the top view while the anti properties happen on the side view. Since they are effectively orthogonal to each other, you can independently control them to a large extent There are limits of course, but they are at the extremes. Most independent suspension designs give you the ability to control these factors independently.
Sir, why is that one arm in the lower wishbone is always perpendicular to the body rather than like in the upper arm where both two arms are in same angle with respect to the body
Hi Hubert,
Thank a lot for your video I finally understood why force would apply at CP on a live axle. 👍
I have one for you:
If the car you draw @6:20 is a RWD with a live rear axle, it would have 100% anti squat. So no squat on power, right?
Now if you draw the Side View Instant Center of the front suspension, the intersection of front and rear SW IC will be the pitch centre, right?
It is totally possible that your pitch centre locates way below the Suspended Mass CoG...
So then if you have a pitch moment, how can you not have squat?🤔
The way I feel it, is that anti effect work according to this definition only if one axle is connected...
Laurent
Laurent, The front suspension IC would only be relevant if there is also drive torque going through the front. But in a RWD car, all the drive torque is going through the rear so there are no forces being applied on the front to help counteract the lift that happens on the front during acceleration due to the weight transfer. That is why on a RWD car, the ideal line does not go through the CG but instead goes through a point at the height of the CG above the front wheel centerline. Remember, the pitch moment comes from a horizontal force acting at the height of the CG. It doesn't care where the CG is longitudinally. It only cares about its height above ground.
@@suspensionsexplained Hubert, I agree but that's not my point.
Let's take this example:
Say you design a RWD car with 100% anti squat.
Make it accelerate from a stop at 1G
Will it squat? supposedly No.....
Design the front suspension so that the Pitch axis is well below the SM_cg.
Now you have a car with 100% anti squat but also a consequent pitch moment arm.
Make it accelerate from a stop at 1G
Will it squat?
No it will not squat, but the front will lift. "Anti" properties (anti-lift, anti-squat, anti-dive) work because they take the horizontal forces (from acceleration or braking) and convert them into vertical forces which counteract the forces from weight transfer. So, if there are no horizontal forces then there cannot be any "anti" forces. What this means is for a RWD car, the front suspension design has no impact on the amount of squat that happens in the rear. All the front suspension does is react to the weight transfer since there are no horizontal forces to counteract it. This means the IC of the front suspension or where it crosses the IC line of the rear suspension is irrelevant. It doesn't matter if this intersection is below the CG or not. All that matters is where the IC line from the rear goes since that is the only place where acceleration forces are coming from.
@@suspensionsexplained Hubert, thank you for your explanations!
But what does the pitch axis do then? Maybe you need to make a new video...😉
The pitch axis is relevant during braking because there are forces coming from both the front and rear suspensions. It can also be relevant during acceleration in an AWD situation but then the lines need to be drawn correctly considering which suspension is a live axle and which one is independent.
If you are in a rear wheel drive would pro-squat not be desirable to get you more traction on the rear wheels?
No, the weight transfer won't increase significantly if at all by having pro squat. You'll just get other undesirable dynamic geometry changes by compressing the rear suspension, like more negetive camber (not good for acceleration) to
Kinda blew my mind that the slot would have more angle, not less, on a split AWD system.. I figured the AWD would squat less to start with, due to less torque being sent to the rear wheels pushing the car down. I am trying to remember if the rear suspension on my AWD E46 is different from the RWD cars, or if it was "close enough for government work" and the parts are all interchangeable. I know the springs are different (mine is on aftermarket H&Rs though) and the dampers might be as well (I have Bilsteins, and when I replaced them due to one of the rears being blown, the new recommendation from Bilstein was to use the E36 M3 dampers out back... the other design was weaker with a smaller rod).
mry82, The "anti" properties of a suspension have the function of taking horizontal forces (like from acceleration or braking) and turning them into vertical forces that counteract the weight transfer force. Since the weight transfer force is a function of the total acceleration or deceleration of the vehicle, the rear suspension in a RWD car will have more force to work with than the rear suspension of an AWD car. This is because in an AWD car, the percentage of acceleration contributed by the rear suspension is less than it would be in a RWD car. This means that the lower amount of acceleration force coming from the rear has to do more work to counteract the weight transfer which is a function of the TOTAL acceleration force.
Thanks for that clear, concise explanation! Looking forward to more videos. @@suspensionsexplained
Thank you for your video, i do have a question, would Anti-Squat affect grip or not? if yes/no, how and why?
by common sense, it seems that if there is Anti-Squat, eventually the tire will took all the force. If not, the suspension can absorb some. so Anti-Squat seems to have negative effect on available grip?
i try to find the answer online for a long time, some say yes, some say no and i still do not get a proper answer.
just to clarify, i am talking about mechanical grip, aero is not considered
The answer to this question is very complicated and not one I have seen much discussion on. I have talked to race car drivers/builders who feel that excessive anti-squat is bad.
Weight transfer will happen regardless of how much anti-squat you have. It is simply a function of the wheelbase, CG height, vehicle weight and acceleration. It has absolutely nothing to do with the suspension. However, the speed at which the weight transfer happens and the speed at which the tires "see" the weight transfer is definitely a function of the suspension. With a lot of anti-squat, the tires see the effect of the weight transfer more quickly. The affect can be that the tires are suddenly hit by the weight transfer and this can upset the tires and make them loose traction. I think this is what the race drivers are talking about. With less anti-squat, the tires will see the effect of the weight transfer more slowly. I have never seen any science behind this though so this is all strictly anecdotal.
@@suspensionsexplained Thank you so much for answering me. For myself, it is harder for me to feel the limit of the tire with a car with high anti-geometry. Especially when turn in with high anti-dive geometry car.
May you talk about anti roll bar in later video? will it affect grip as well?
For example comparing a car with both big anti roll bar front and rear with a car with small anti roll bar front and rear.
Thanks once again. What do they say? "If I knew then what I know now". (-;
Wow, Ok just Wow but, I have questions; "The "anti's" are very important for a super high horse-power vehicle. How do you weight the value of anti-squat over a spectrum of vehicles say, Dragster to a truck for hauling to a 4WD off road vehicle?" How does one adjust the instant center goals for these vehicles? There are drag enthusiasts who explain what they need to race but, the concepts are never adjusted from 2000HP drag car to a 600HP 4WD truck. And AWD car has a torque distribution but, a real 4WD truck is most often only 2WD at 0% torque distribution. What are your thoughts on this? I understand how to maintain pinion angle but, that isn't the whole story. That effort must be balanced with concerns about instant center location. This is quite a balancing act. I did notice that the upper A frame of my 2500 was not parallel to the lower and I thought "WHAT". Now I see why. The A frame pair have their own instant center and if they were parallel the axis lines would never intersect. Same is true with a 4-link rear suspension. If each pair of links, upper and lower were parallel the pinion angle would be maintained over the range of travel but there would not be any projected instant center for the rear suspension. Now that I am a "wise-idiot" I'd love to know more about how to balance all this.
So, does it actually reduce load transfer?
god damn , so i basically designed everything wrong but the car is already built .... also , can u be my dad ? :)
I'd love to be your dad, but you'll have to get past your would-be siblings first. The interview process is hell!!
Mbac i pil da minc
Sloppy explanation. Have no idea what he's talking about.